Primary biliary cholangitis and Sjogren's syndrome: bi-directional Mendelian randomization analysis

Observational studies have shown a higher prevalence of Sjogren's syndrome (SjS) in patients with primary biliary cholangitis (PBC) than in the healthy population, but whether this correlation is causal needs further confirmation. This study aimed to investigate the bidirectional causal relationship between PBC and SjS using Mendelian randomization (MR) analysis.

We used pooled data from a large-scale genome-wide association study (GWAS) to select mutually independent genetic loci associated with PBC and SjS in people of European ancestry as instrumental variables (IVs). The causal association between PBC and SjS was analyzed by MR analysis using inverse variance weighting (IVW) and weighted median methods, and the ratio of ratios (OR) was used as an evaluation index. In addition, sensitivity analyses, including Cochran's Q test, MR-PRESSO, MR-Egger intercept test, and leave-one-out test, were performed to ensure the stability of the results.

A total of 20 validated IVs were selected for PBC, and the number of IVs for SjS was seven. Positive MR analysis showed that genetically predicted PBC was significantly associated with the risk of SjS (IVW OR=1.174, 95% CI: 1.107-1.246, p<0.001). The weighted median method further confirmed this result (OR=1.146, 95% CI: 1.053-1.247, p=0.016). Inverse MR analysis showed that genetic susceptibility to SjS also increased the risk of PBC (IVW OR=1.737, 95% CI: 1.280-2.357, p<0.001), and this result was also confirmed by the weighted median method (OR=1.398, 95% CI: 1.120-1.746, p=0.003).

Our study found that genetically predicted SjS increased the risk of PBC and vice versa in a European population. This may shed light on the etiology of PBC and the management of patients with SjS.